Ok - This problem is happening on a Renault 5 GT with a Rover T25 turbo.

When I put my foot down @ 2k to 3k, the the boost gauge only moves from @-20In.Hg vacuum to 0 psi and stays like this all the way up the rev range.

The wastegate has been fitted from a T2/T25 hybrid and is set @ 15psi and was working before.

There is no white or blue smoke, the turbine wheel spins freely and there appears to be no play in the shaft. No obvious leaks or hose splits either.

Any ideas?